1. Field of the Invention
The present invention relates to a method for manufacturing an electrophotographic photosensitive member (hereinafter referred to as “a-Si photosensitive member” as well) having a photoconductive layer (hereinafter referred to as “a-Si photoconductive layer” as well) formed from amorphous silicon (hereinafter referred to as “a-Si” as well), which can be applied to an image-forming apparatus (electrophotographic apparatus) using an electrophotographic process such as a copying machine, a printer and a facsimile.
2. Description of the Related Art
An electrophotographic photosensitive member is widely known, which is made by forming a photoconductive layer (photosensitive layer) consisting of an amorphous material on a conductive substrate (hereinafter referred to as merely “substrate” as well). An a-Si photosensitive member has already been commercialized, which has a photoconductive layer formed on the substrate such as metal with a film-forming technology (layer-forming technology) such as a chemical vapor deposition method (CVD method) and a physical vapor deposition method (PVD method), in particular.
The structure of a positively chargeable a-Si photosensitive member 5000 as illustrated in FIG. 5A and the structure of a negatively chargeable a-Si photosensitive member 5100 as illustrated in FIG. 5B are known as basic structures of the above described a-Si photosensitive member.
The positively chargeable a-Si photosensitive member 5000 has a layer structure of forming a light receiving layer 5002 formed from a-Si on a conductive substrate 5001, and further stacking a surface layer 5005 thereon which is formed from hydrogenated amorphous silicon carbide (hereinafter referred to as “a-SiC” as well). The light receiving layer 5002 may also have a stacked structure of a lower electric-charge injection preventing layer 5003 and a photoconductive layer 5004.
The negatively chargeable a-Si photosensitive member 5100 has a layer structure of forming a light receiving layer 5102 formed from a-Si on a conductive substrate 5101 and further stacking a surface layer 5105 thereon which is formed from a-SiC. The light receiving layer 5102 may also have a stacked structure of a lower electric-charge injection preventing layer 5103, a photoconductive layer 5104 and an upper electric-charge injection preventing layer 5110.
An a-SiC surface layer has been mainly used in an electrophotographic apparatus with a fast processing speed because of having a superior abrasion resistance. However, a surface layer conventionally formed from a-SiC (hereinafter referred to as “a-SiC surface layer” as well) has occasionally caused a problem that when used in an environment of high absolute humidity, letters are blurred or the letters form a blank area without being printed (hereinafter referred to as “high-humidity flow”).
The high-humidity flow (or image flow or image deletion due to high-humidity) means a phenomenon as will be described below.
Specifically, the high-humidity flow occurs when an image has been output with the use of an electrophotographic apparatus placed in the environment of high absolute humidity and an image is output again after a while, and indicates such an image failure shown in the latter output image that letters are blurred or form a blank area without being printed.
This high-humidity flow is considered to be caused by a phenomenon that the surface resistance decreases due to moisture adsorbed on the surface of the electrophotographic photosensitive member and electric charges flow transversely. Therefore, the high-humidity flow more easily occurs when the electrophotographic apparatus is placed in the environment of high absolute humidity or does not have a heater for heating the photosensitive member provided in the vicinity of the a-Si photosensitive member. Accordingly, in order to inhibit the occurrence of this high-humidity flow, it has been carried out to reduce or remove an electrification product or moisture, which has been adsorbed on by the surface of the electrophotographic photosensitive member and is considered to cause the high-humidity flow, by always heating an electrophotographic photosensitive member with the use of the heater for heating the photosensitive member.
In contrast to this, a large number of electrophotographic processes are conventionally proposed in order to inhibit the high-humidity flow with other methods than using a heater for heating the photosensitive member.
On the other hand, there are proposed a large number of a-Si photosensitive members and manufacturing methods therefor, which aim at inhibiting the high-humidity flow by reducing the adsorption of an electrification product or moisture and enhancing the removal efficiency.
Japanese Patent Application Laid-Open No. H09-204056 discloses a technology of controlling a surface layer made from a-SiC which is stacked on a photoconductive layer and is expressed by a composition formula of a-Si1-xCx:H so as to have an element ratio of 0.95≦x≦1.00 when expressed by the value x, and controlling a dynamic pushing hardness of the free surface to 45 to 220 kgf/mm2.
According to this technology, the surface layer acquires low hardness by controlling the value x to 0.95 or more, and becomes easily abraded. As a result, an adsorbed material such as an electrification product and moisture adsorbed on the surface of the surface layer together with an oxidation modified part on the surface can be removed, and accordingly the high-humidity flow can be inhibited.
Japanese Patent Application Laid-Open No. 2002-123020 discloses a technology of composing the surface layer of a negatively chargeable a-Si photosensitive member having an a-Si photoconductive layer and an a-SiC surface layer sequentially stacked on a substrate so as to make carbon atoms in the surface layer ununiformly distributed in a stacked direction and give the content of the carbon atoms a local maximum value in a region except the surface.
According to this technology, a light career is recombined with a surface charge in the vicinity of the top surface side of a region in which the content of the carbon atoms becomes maximum, so that the recombination is not affected by the electrification product adsorbed on the surface, which can inhibit the high-humidity flow.
In recent years, in the market, the printing process is changed to an electrophotographic process in which the surface layer is further easily abraded compared to a conventional electrophotographic process along with the tendency of the speedup and colorization of an electrophotographic apparatus. Along with the tendency of the speedup and colorization, an electrophotographic apparatus is also required which can stably output an image of high quality. Furthermore, the market shows a keen interest in an environmental problem, and the electrophotographic apparatus is also required to have enhanced energy-saving properties by decreasing an electric power consumption.
For these market requests, the electrophotographic apparatus itself needs to be improved as well. At the same time, an electrophotographic photosensitive member is also required to have an improved high-humidity flow while maintaining adequate abrasion resistance and further have superior energy-saving properties as well.
However, the technology in Japanese Patent Application Laid-Open No. H09-204056 has needed a certain amount or more of abrasion so as to remove an oxidized layer formed on the surface of the electrophotographic photosensitive member and an adsorbed material which causes the high-humidity flow and is represented by moisture and the electrification product adsorbed on this oxidized layer, in order to inhibit the occurrence of the high-humidity flow.
When the technology in Japanese Patent Application Laid-Open No. H09-204056 is not used, the electrophotographic photosensitive member has enabled the high-humidity flow to be inhibited while controlling the abrasion amount, by making a heater for heating the photosensitive member provided in the vicinity of the electrophotographic photosensitive member, and thereby removing the moisture adsorbed on the surface of the electrophotographic photosensitive member.
However, the heater for heating the photosensitive member needs a large amount of an electric power, so that when the heater for heating the photosensitive member is used, it is difficult to reduce the power consumption.
From the above description, it has been a very difficult problem for a conventional electrophotographic photosensitive member and electrophotographic apparatus to realize both of enhancing the abrasion resistance and reducing the power consumption while inhibiting the high-humidity flow.
In addition, it is extremely important for the a-SiC surface layer to inhibit the oxidation of the a-SiC surface layer, which affects the adsorptivity for the adsorbed material, in order to inhibit the high-humidity flow. The a-SiC surface layer also needs to enhance its hardness in order to enhance its abrasion resistance. Therefore, it is necessary to enhance the denseness of a-SiC itself which forms the surface layer, in order to inhibit the high-humidity flow and simultaneously enhance the abrasion resistance.
It is considered as a method of preparing an a-SiC surface layer having such high denseness to promote the decomposition of a source gas. As for its specific technique, it is considered to increase a high-frequency power to be introduced into a reaction vessel compared to a conventional technique, or to reduce an amount of the source gas to be supplied.
However, there is a case in which the ratio of a number of atoms of carbon atoms with respect to the sum of the number of atoms of silicon atoms and the carbon atoms in the surface layer (hereinafter referred to as “C/(Si+C)” increases when the high-frequency power to be introduced into the reaction vessel is simply increased compared to the conventional technique, and the light absorption at the a-SiC surface layer increases. In such a case, an amount of an image-exposing light necessary for forming an electrostatic latent image increases, and the sensitivity is lowered.
There is also a case in which the C/(Si+C) in the surface layer increases even when the amount of SiH4 to be supplied is extremely decreased, and the sensitivity is lowered by the increase of the light absorption.
On the other hand, when the amount of CH4 to be supplied is extremely reduced, the resistance of the a-SiC surface layer decreases, and accordingly a carrier easily causes a transverse flow in the surface layer when the electrostatic latent image is formed. Therefore, when isolated dots are formed for the electrostatic latent image, the isolated dots become small due to the transverse flow of the carrier in the surface layer. As a result, an image concentration decreases particularly in a low concentration side of an output image, so that there is a case in which the gradation properties decreased.
In addition, there is a case in which hydrogen atoms are overly reduced in the surface layer by an excessive decomposition of the source gas depending on a manufacturing condition, even when the C/(Si+C) of the a-SiC surface layer is controlled to an appropriate range. In such a case, it becomes difficult to keep the sensitivity adequate.
As was described above, it has been very difficult to prepare the a-SiC surface layer having all of high-humidity flow, an abrasion amount, gradation properties and sensitivity controlled to an adequate state, and the realization technique has not been found.